研究目的
To extend the range of reliable measurements by using several light sources without reducing the resolution and scaling of the error in interference measurements of surface nanotopography.
研究成果
The differential topography method extends the measurement range by more than a factor of 5 without reducing resolution. The three-wavelength method further increases the range, allowing measurements up to ～7 μm with low error. Field experiments confirm the methods' effectiveness in resolving phase ambiguity and providing reliable surface topography measurements, validated by comparisons with commercial equipment.
研究不足
The measurement range is limited by the coherence length of the light sources (～7 μm for the LEDs used). The accuracy depends on the measurement error, with larger errors reducing the effective range. The methods require precise wavelength knowledge and may be sensitive to environmental changes and actuator reproducibility.
1：Experimental Design and Method Selection:
The study employs phase-shifting interferometry (PSI) with multiple wavelengths to overcome phase ambiguity. Methods include differential topography using two wavelengths and a three-wavelength approach. Algorithms for calculating measurement ranges based on wavelengths and errors are developed.
2：Sample Selection and Data Sources:
Samples with stepped structures and smooth height changes are used, with heights around
3：9 μm and 2 μm, and roughness Sa less than 4 nm. List of Experimental Equipment and Materials:
MNP-1 interference microscope, three LEDs with wavelengths λ1=
4：39 nm, λ2=47 nm, λ3=18 nm, mixed fiber, piezoceramic actuator, CCD camera, commercial spectrometer, lasers (He–Ne laser at 633 nm, laser pointer at 532 nm, DHOM laser at 473 nm), and a commercial interference microscope for comparison. Experimental Procedures and Operational Workflow:
6 Light from LEDs is coupled into the interferometer via mixed fiber. Scanning is performed over 1 μm with 256 interferograms recorded per wavelength. Phase shifts are determined by minimizing standard deviation between correlograms. Measurements are conducted in two-wavelength and three-wavelength modes, with results compared to a commercial microscope.
5：Data Analysis Methods:
Height differences are calculated using Δh = λΔΦ/4π. For multiwavelength methods, algorithms involve calculating auxiliary quantities, iterating over possible phase jumps, and minimizing differences between heights. Numerical experiments and field data are analyzed to determine measurement ranges and errors.
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MNP-1 interference microscope
MNP-1
Used for interference measurements of surface topography with multiple light sources.
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LED
Light sources with specific wavelengths (629.39 nm, 534.47 nm, 467.18 nm) for generating interferograms.
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mixed fiber
Couples light from multiple sources into the interferometer.
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piezoceramic actuator
Used for phase scanning by moving the mirror in the reference arm of the interferometer.
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CCD camera
Records interferograms for analysis.
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commercial spectrometer
Measures the wavelengths of the LEDs.
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He-Ne laser
Used for wavelength correlation in the Fourier spectrometer mode.
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laser pointer
Used for wavelength correlation in the Fourier spectrometer mode.
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DHOM laser
Used for wavelength correlation in the Fourier spectrometer mode.
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commercial interference microscope
Used for comparative measurements to validate the proposed methods.
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